This invention relates generally to the implantation of substrates. More particularly, the present invention relates to a modulated plasma potential ion implantation system used for the fabrication of solar cells and flat panel devices.
Ion implantation is a standard technique for introducing property-altering impurities into substrates. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the substrate. The energetic ions in the beam penetrate into the sub-surface of the substrate material and are embedded into the crystalline lattice of the substrate material to form a region of desired conductivity or material property.
Localized or selective doping or localized or selective material modification may be required for some implants. For example, fabrication of solar cell devices and/or manufacturing of flat panel devices present examples in which high dose implantation and selective doping of local areas is desirable. These high dose implantation applications require relatively high-throughput to provide an alternative to competitive fabrication techniques and systems and to contribute to the lowest cost-of-ownership for an ion implantation system. However, high-volume production for implant applications for these devices confronts significant challenges due, in part, to “glitching” in the extraction region. Generally, “glitching” refers to the interruption in beam current of an ion beam incident on a surface of a substrate. More particularly, glitching is a sudden transient in the beam current that may adversely affect dose uniformity of implant species on a target substrate.
Certain ion implantation systems used for the manufacture of solar cells suffer from a lack of suppression in the extraction region where plasma in the source chamber is coupled with the ions incident on the surface of a substrate. This may cause source instability, glitching and beam current drift. To correct for these challenges, some ion implantation systems utilize various extraction electrode configurations including, for example, a suppression electrode, a focus electrode and a ground electrode to control the extracted beam quality and to suppress unwanted glitching. Although adding these components may mitigate these challenges, it also adds to system complexity and adversely affects cost of ownership of these implanters used for high-volume production. Accordingly, there is a need in the art for an improved implantation of workpieces and, more particularly, to an improved method and apparatus for implantation of substrates while avoiding ion beam glitching.